High-rise buildings, power stations, various industrial plants, vehicles and ships are constantly exposed to fire hazards, so with respect to the wire harnesses installed in these structures, the need has recently arisen to use electric wires and cables that employ insulation or sheath materials that are highly resistant to flame and which will not evolve halide gases, as they burn, that are harmful to humans and capable of causing corrosion of surrounding instruments.
U.S. Pat. No. 4,067,847 describes a flame retardant (self-extinguishing) resin composition prepared by incorporating a metal hydroxide such as magnesium hydroxide, and preferably additional carbon black, into a polyolefin such as polyethylene, polypropylene or a propylene-ethylene copolymer. The metal hydroxide used there will release the water of crystallization by heat of combustion, which fact accelerates the endothermic reaction, to thereby render the resin resistant to flame. By using this flame retardant resin composition as an insulation or sheath material, electric wires or cables having low smoking properties and evolving no toxic gaseous components can be realized. In this respect, the recipe disclosed in U.S. Pat. No. 4,067,847 holds much promise for applications where high flame resistance is required.
On the other hand, electric wires and cables are often laid in poorly ventilated areas such as cable tunnel or ducts or are buried under the ground, and it have recently become apparent that materials containing polyolefins and metal hydroxides as basic components easily suffer from the generation of fungi. The exact mechanism of the generation of fungi has not been fully elucidated but in consideration of the fact that the generation of fungi is negligible when polyolefins are used alone, it can be supposed that the absorption of water or moisture or the surface unevenness caused by the addition of metal hydroxides which relate to implantation of fungi.
There is another problem that is perculiar to those flame retardant electric wires and cables which are especially intended for use in vehicles and ships. It has recently been required to provide them not only with fungus resistance but also with oil resistance comparable to that of neoprene rubber and chlorosulfonated polyethylene in order to ensure satisfactory field performance.